Esters of polyvalent alcohols, process for preparing them and their use as lubricating oils

ABSTRACT

As new industrial products, the esters of the following general formula (A) ##STR1## in which R 1  is alkyl radical selected from the group consisting of  hyl and ethyl; 
     R 2  is an alkyl radical selected from the group consisting of methyl and ethyl; and 
     R 3  is an alkyl radical having the formula C n  H 2n+1  wherein n is a number from 5 to 11. 
     Process for the preparation of said esters as well as their use in the field of lubrication, of hydraulic fluids, of oily emulsions and of thermal fluids.

The present application is a continuation in part of the copending application No. 382,757 filed on May 27, 1982, abandoned which is a continuation of application No. 181,280 of the same Applicant, filed on Aug. 25, 1980 abandoned.

BACKGROUND OF THE INVENTION

The present invention refers to esters with a mixture of polyhydroxyl alcohols, hexahydrobenzoic acid and a linear carboxylic acid as new industrial products.

The present invention further refers to a process for the preparation of said esters, as well as to their use in the field of lubrication, hydraulic fluids, oily emulsion, and thermal fluids, and in particular to the so-called EP (extreme pressure) fluids.

The use of synthetic lubricants based on long chain, linear aliphatic esters of pelargonic acid, lauric acid, palmitic acid, etc., is known; however, since said acids are of natural origin, their price is relatively high and therefore the lubricating oils obtained therefrom can hardly compete with the mineral oils from oil from an economic viewpoint. Attemps have been also made to obviate this drawback by using e.g. benzoic acid esters which are much cheaper. These esters, however, have not been successful because of a number of drawbacks, such as e.g. that in combustion engines they form partially incombustible products, whereby they produce highly smoky products in the discharge gases. A further drawback is that the lubricating power and especially the viscoelasticity of benzoic acid based esters is relatively not good.

SUMMARY OF THE INVENTION

The Applicant has now surprisingly found a new class of esters, better to be specified hereinafter, of polyhydroxyl alcohols with a mixture of hexahydrobenzoic acid and a linear carboxylic acid, having characteristics of viscosity and stability such that they can be successfully employed in the field of lubricants, of hydraulic fluids, of oily emulsions, of thermal fluids, and particularly in the field of the so-called EP fluids and so on.

More particularly they can be successfully used in lubricating compositions having improved features regarding a high detergency and a lower loss of viscosity during prolonged use.

The new class of esters can be defined by the following general formula (A): ##STR2## in which R₁ is an alkyl radical selected from the group consisting of methyl and ethyl; R₂ is an alkyl radical selected from the group consisting of methyl and ethyl; and R₃ is an alkyl radical having the formula C_(n) H_(2n+1) wherein n is a number from 5 to 11.

Obviously n is not always a whole number but in some instances it can also be a decimal number, such as 8.33, 8.66, 10.33, 10.66 and so on.

Preferably R₃ is --C₈ H₁₇ or --C₁₁ H₂₃.

The present invention further relates to a process for the preparation of the esters of general formula (A). Said process is characterized by the fact that an alcohol of the formula ##STR3## wherein R₁ and R₂ have the same meaning as given in the general formula (A), is reacted with a stoichiometric amount of an essentially equimolar mixture (B) consisting of hexahydrobenzoic acid and an acid of the formula R₃ --COOH, wherein R₃ has the same meaning as defined in the general formula (A).

By essentially equimolar it is meant that from 0.95 to 1.05 moles of the linear acid (R₃ --COOH) is used for each mole of the hexahydrobenzoic acid.

The preparation of these esters may be carried out by mixing the components and heating the mixture to the suitable temperature, in the presence or in the absence of an azeotropism agent in order to eliminate more easily and continuously the water which is produced in the reaction.

When toluene is used as an agent for promoting the separation of the water from the system, it is necessary to employ such an amount as is sufficient to maintain the reaction temperature at the desired value. E.g., to maintain a temperature of 200° C., from 10 to 100 g of toluene should be used per 1 kg of reaction mass (acids plus alcohol).

It is possible, as already mentioned, to employ a slight excess of one of the components of the acid mixture with respect to the theoretical value calculated from the number of the OH groups in the alcohol or mixture of alcohols. In general, it is convenient to use a slight excess of the linear acid with respect to the hexahydrobenzoic acid.

The esterification may be carried out discontinuously or continuously, in the presence or in the absence of the conventional esterification catalysts.

The reaction times suitably vary from 5 to 50 hours, depending on whether a catalyst is used.

Of course when no catalysts are used, it is convenient, because of the longer reaction times, to operate discontinuously, while when catalysts, such as sulphuric or phosphoric acid, are used, it is convenient to operate continuously.

Hereinafter a way of preparing the esters of formula (A) will be described, which obviously is to be considered as illustrative and not limitative.

The reaction mixture containing the alcohol and both the linear as well as the hexahydrobenzoic acid in essentially equimolar amounts, is conveniently heated to 195° C., and said temperature is maintained for a period from 2 to 8 hours, whereafter the toluene is added in an amount from 0.1 to 1.0% by weight with respect to the reaction mass, and the heating is then continued until the discharge of water comes to an end. The excess of carboxylic acid and azeotropism agent, if any, may be removed under a vacuum.

The present invention relates also to the use of at least one of the esters of general formula (A) in the field of lubrication, hydraulic fluids, oily emulsions, thermal fluids, EP fluids and the like. By the use of such esters as lubricants, the main disadvantages and/or drawback which have been mentioned hereinbefore, in the use of the synthetic esters known in the art, are eliminated.

The esters according to the invention exhibit a low viscosity (e.g. less than 10 cSt at 100° C.) whereby they can be successfully employed in mixture with paraffin oils wherein the more volatile portion (which generally assists in decreasing the viscosity of the oil) has been substituted with the esters of general formula (A) having a low viscosity but a relatively higher volatility.

Although the good characteristics of the esters of linear chain acids are maintained and generally increased, the use of the esters of general formula (A) avoids the bad combustion of the known esters based on benzoic acid and in general on aromatic compounds, and further, a low cost product is provided which may compete with the mineral oils.

In the lubrication field, the esters of general formula (A) may be employed alone, in admixture with each other, in admixture with other known synthetic esters or with known lubricants derived from mineral oils, both in "internal" lubrication of internal combustion engines or of turbines, and in the lubrication of parts which do not come into contact with the vessel in which the combustion occurs.

The esters of general formula (A) may be used as a lubricant base, also in a mixture with mineral oils derived from crude oil, e.g. by using a weight ratio of the ester of general formula (A) to the mineral oil between 99:1 and 20:80.

It is further convenient to add the normal additives which improve the viscosity index, detergent, dispersion promoting, antifoaming additives, etc., in ratios and overall amounts which range from 0 to 25% referred to the ester or, when the mineral oil derived from crude oil is present, to the mixture of esters and mineral oil.

In the lubrication of internal combustion engines, they may be employed in the so-called two-stroke cycle engines in which, in general, the lubricant is mixed with the fuel and is burnt or expelled with the combustion gases.

Since these esters do not contain sulphurated products or aromatic hydrocarbons which leave behind or emit carbon particles or acidic compounds (inorganic compounds derived from sulphur) both the cleanliness of the engine and the ambient pollution conditions are improved. If they are used in the cutting oils, they do not discharge aromatic hydrocarbons into the workroom.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the change in viscosity during use in an engine of a lubricant oil containing an ester in accordance with the present invention compared with an oil not containing the present ester.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples are illustrative but not limitative. (The parts are by weight unless otherwise specified).

EXAMPLE 1

Preparation of the ester of formula: ##STR4##

1040 g of neopentylglycol, 1340 g of hexahydrobenzoic acid, 2000 g of lauric acid and 100 g of toluene are heated to 190°-200° C. in inert atmosphere and under atmospheric pressure, removing continuously the azeotropism agent H₂ O (of reaction)--toluene and, after elimination of the water, recycling the toluene. After about 30 hours the reaction is practically completed, the excess of acid and the low-boiling products are removed by distillation under reduced pressure (3-5 mm Hg) until having in the tail-product a residue acidity of 0.002 meq/g.

The average chemical-physical characteristics of the obtained product are:

    ______________________________________                                         kinematic viscosity at 40° C. (ASTM D 445), cSt                                                     16.7                                               kinematic viscosity at 100° C. (ASTM D 445), cSt                                                    4.0                                                viscosity index (ASTM D 2270)                                                                              136                                                pour point, °C. (ASTM D 97)                                                                         -9                                                 flash point, OC, °C. (ASTM D 92)                                                                    220                                                evaporation loss at 250°  C., % (DIN 51581)                                                         13.5                                               density at 19° C.    0.95                                               ______________________________________                                    

EXAMPLE 2

Preparation of the ester of formula: ##STR5##

1040 g of neopentylglycol, 1340 g of hexahydrobenzoic acid, 1580 g of pelargonic acid and 100 g of toluene are reacted and distilled as in the foregoing example.

The average chemical-physical characteristics of the obtained product are:

    ______________________________________                                         kinematic viscosity at 40°  C. (ASTM D 445), cSt                                                    12.8                                               kinematic viscosity at 100° C. (ASTM D 445), cSt                                                    3.2                                                viscosity index (ASTM D 2270)                                                                              116                                                pour point, °C. (ASTM D 2270)                                                                       -64                                                flash point, OC, °C. (ASTM D 92)                                                                    207                                                evaporation loss at 250° C., % (DIN 51581)                                                          25.0                                               density at 19° C.    0.97                                               ______________________________________                                    

EXAMPLE 3

A lubricating oil prepared with 63.4% (by weight) of mineral bases SN containing 10% of trimethylolpropane tripelargonate and 10% of neopentylglycol monohexahydrobenzoate monolaurate and with the same additives and in the same quantity as those used in the subsequent example, is submitted to the same working tests disclosed in the subsequent example No. 4.

The chemical-physical characteristics of the oil, before and after the test are reported in the table

    ______________________________________                                                               Before                                                                               After                                                                    the test                                                                             the test                                           ______________________________________                                                                         (120                                                                           hours)                                         kinematic viscosity at 100° C. (ASTM D 445)                                                     17.2    14.3                                           kinematic viscosity at 40° C. (ASTM D 445)                                                      108.8   88.9                                           dynamic viscosity at -18° C. (calculated)                                                       4000    2980                                           viscosity index (ASTM D 2270)                                                                           171     164                                           flash point (OC), °C. (ASTM D 92)                                                                225°                                                                            220°                                   density at 18° C.                                                                               0.90    0.90                                           volatility at 250°, NOACK (DIN 51581), %                                                        8.1     8.5                                                                            (96                                                                            hours)                                         Content in Fe (ppm)     3.2     39.7                                           Content in Cr (ppm)     0.2     0.2                                            Content in Mn (ppm)     0.2     0.5                                            Content in Cu (ppm)     0.9     9.8                                            Content in Pb (ppm)     1.7     5.6                                            Content in Al (ppm)     1.0     1.0                                            ______________________________________                                    

The viscosity changes during prolonged use as indicated in FIG. 1.

EXAMPLE 4

A lubricating oil, prepared with 63.4% (by weight) of mineral bases SN and 20% of trimethylolpropane tripelargonate, and therefore not containing any of the esters of the general formula (A), the amount to 100 being constituted by the packet of additives for gasoline engine oil, and by the viscosity index improver, has been submitted to a discontinue working test (cycles of about 12 hours) for 120 total hours on a Petter engine (Diesel, monocylindrical, four-stroke) using as fuel a gas oil with high sulphur content (about 2%).

The chemical-physical characteristics of the oil, before and after the test are reported in the table:

    ______________________________________                                                               Before                                                                               After                                                                    the test                                                                             the test                                           ______________________________________                                                                         (120                                                                           hours)                                         kinematic viscosity at 100° C. (ASTM D 445)                                                     17.3    13.5                                           kinematic viscosity at 40° C. (ASTM D 445)                                                      108.2   82.2                                           dinamic viscosity at -18° C. (calcolated)                                                       3450    2760                                           viscosity index (ASTM D 2270)                                                                           172     164                                           flash point (OC), °C. (ASTM D 92)                                                                227     225                                           density at 18° C.                                                                               0.90    0.90                                           volatility at 250°, NOACK (DIN 51581), %                                                        6.4     7.7                                                                            (96                                                                            hours)                                         Content in Fe (ppm)     5.2     43.5                                           Content in Cr (ppm)     0.2     0.2                                            Content in Mn (ppm)     0.4     0.7                                            Content in Cu (ppm)     1.4     10.7                                           Content in Pb (ppm)     1.9     5.9                                            Content in Al (ppm)     1.0     1.0                                            ______________________________________                                    

The viscosity changes during prolonged use as indicated in FIG. 1.

EXAMPLE 5

(comparative example with example 1)

Example 1 is repeated using a molar ratio of hexahydrobenzoic acid:lauric acid equal to 0.45:0.55.

The average chemical-physical characteristics of the obtained products are the following:

    ______________________________________                                         kinematic viscosity at 100° C. (ASTM D 445), cSt                                                    4.0                                                viscosity index (ASTM D 2270)                                                                              125                                                pour point, °C. (ASTM D 97)                                                                         0                                                  NOACK                       14.5                                               ______________________________________                                    

EXAMPLE 6

(comparative example with example 1)

Example 1 is repeated using a molar ratio of hexahydrobenzoic acid:lauric acid equal to 0.55:0.45.

The average chemical-physical characteristics of the obtained product are the following:

    ______________________________________                                         kinematic viscosity at 100° C. (ASTM D 445.), cSt                                                   3.9                                                viscosity index (ASTM D 2270)                                                                              140                                                pour point, °C. (ASTM D 97)                                                                         -5                                                 NOACK                       12.5                                               ______________________________________                                    

As the two comparison examples 5 and 6 clearly show by not keeping the molar ratio of 0.5, the pour point characteristic is worse.

EXAMPLE 7

(comparative example with example 2)

Example 5 is repeated substituting lauric acid with pelargonic acid. pelargonic acid.

The average chemical-physical characteristics of the obtained product are the following:

    ______________________________________                                         kinematic viscosity at 100° C. (ASTM D 445), cSt                                                    3.4                                                viscosity index (ASTM D 2270)                                                                              100                                                Pour point, °C. (ASTM D 97)                                                                         -40                                                NOACK                       25                                                 ______________________________________                                    

EXAMPLE 8

(comparative example with example 2)

Example 6 is repeated substituting lauric acid with pelargonic acid.

The average chemical-physical characteristics of the obtained product are the following:

    ______________________________________                                         kinematic viscosity at 100° C. (ASTM D 445), cSt                                                    3.1                                                viscosity index (ASTM D 2270)                                                                              118                                                pour point, °C. (ASTM D 97)                                                                         -45                                                NOACK                       28                                                 ______________________________________                                    

Also these comparison Examples 7 and 8 clearly show that the characteristic which decreases in an essential way in respect with the examples 1 and 2 is the pour point. 

We claim:
 1. An ester of the general formula (A) ##STR6## in which R₁ is an alkyl radical selected from the group consisting of methyl and ethyl;R₂ is an alkyl radical selected from the group consisting of methyl and ethyl; and R₃ is an alkyl radical having the formula C_(n) H_(2n+1) wherein n is a number from 5 to
 11. 2. An ester having the formula ##STR7##
 3. An ester having the formula ##STR8##
 4. A process for the preparation of an ester of the general formula (A) as defined in claim 1, said process comprising reacting, by heating at a temperature up to 200° C. sufficient to cause esterification, for a duration of from 5 to 50 hours, an alcohol of the formula ##STR9## wherein R₁ and R₂ have the same meaning as given in claim 1, with a stoichiometric amount of an essentially equimolar mixture (B) consisting of hexahydrobenzoic acid and an acid of formula

    R.sub.3 --COOH

wherein R₃ has the same meaning as given in claim
 1. 5. A process according to claim 4 wherein the mixture (B) contains from 0.95 to 1.05 moles of R₃ --COOH for each mole of hexahydrobenzoic acid.
 6. A base for lubricating oils, said base comprising at least one ester of the general formula (A) ##STR10## in which R₁ is an alkyl radical selected from the group consisting of methyl and ethyl;R₂ is an alkyl radical selected from the group consisting of methyl and ethyl; and R₃ is an alkyl radical having the formula C_(n) H_(2n+1) wherein n is a number from 5 to
 11. 7. A base for lubricating oils, said base comprising an ester of the formula ##STR11##
 8. A base for lubricating oils, said base comprising an ester of the formula ##STR12##
 9. A base for lubricating oils according to claim 6, additionally containing other lubricating oils.
 10. A base for lubricating oils according to claim 6, additionally containing at least one normal, viscosity index improving additive, detergent, dispersing and/or antifoaming additive.
 11. A base for lubricating oils according to claim 9, additionally containing at least one normal, viscosity index improving additive, detergent, dispersing and/or antifoaming additive. 